The present invention relates to the use of double-ended, double roller pistons in single-ended barrel engines.
An engine with the ability to vary its compression ratio during operation can significantly improve efficiency and power density for compression-ignited (CI), stoichiometric spark-ignited (SSI), homogeneous charge compression-ignited (HCCI) and lean combustion spark-ignited (LCSI) applications. Variable compression ratio (VCR) abilities allow an engine""s compression ratio to be lowered during high load conditions to prevent detonation or to limit peak cylinder pressure and allow the compression ratio to be raised to improve thermal efficiency at lower load conditions. Variable compression ratio can also be used to phase or supplement the phasing of combustion in homogeneous charge compression engines and to broaden the range of air-fuel ratio that can be used in lean combustion spark-ignited engines. In nearly all engine applications, variable compression ratio is especially beneficial when used in combination with supercharging, where the combination of variable compression ratio and supercharging substantially multiplies the benefits of both features.
In spite of their benefit and applications, engines with variable compression ratio abilities have not been used in commercial applications due to issues of extreme complexity, lack of long-term durability and prohibitively high costs. Several approaches to varying compression ratio in conventional slider-crank engines have been proposed and in some cases have been implemented. One type of variable compression ratio device for use in slider-crank engines is shown in the following publications: PCT Publication No. WO 92/09798, PCT Publication No. WO 92/09799, U.S. Pat. No. 5,329,893; and U.S. Pat. No. 5,443,043, all of which are assigned to Saab. The Saab design includes a traditional in-line slider-crank engine in which the head and cylinder bank are tilted to vary compression ratio. The design preferably also includes an external supercharger for providing boost air to the engine. Using stoichiometric spark-ignition, the Saab variable compression ratio engine has demonstrated a 30% improvement in fuel economy in combined city and highway driving cycles. In spite of its benefits, Saab""s pivoting head design is cumbersome and complex, has potential sealing issues and is prohibitively expensive. Other attempts to vary compression ratio in conventional slider-crank engines are generally inferior to the Saab technique for various reasons.
Another means of varying compression ratio in slider-crank engines is achieved through variable valve timing. Variable valve timing is a very good technology for extending an engine""s torque curve over a broad range of engine speed and for some Miller cycle variable compression ratio applications. However, the usefulness of variable valve timing for other variable compression ratio applications is very limited. Varying compression ratio with variable valve timing relies on decreasing the effective stroke of the engine to lower compression ratio. This results in significant penalties in the effective displacement of the engine as compression ratio is lowered. In nearly all variable compression ratio applications, compression ratio must be lowered when peak power is needed. A reduction in the effective engine displacement at this time significantly reduces the peak power capability of the engine and usually offsets any benefits that can be gained by a varying compression ratio.
In contrast to conventional slider-crank engines, single-ended barrel engines by nature provide a structure that is better suited to utilize a simple and effective means of varying compression ratio. The engine structure of a single-ended barrel engine allows the engine""s compression ratio to be easily and simply varied by axially changing the position of the engine""s central track or cam drive mechanism. By moving the track axially, the pistons can be brought closer to or further away from top dead center (TDC), thus, varying the engine""s compression ratio. This method of varying compression ratio is both durable and inexpensive and is more effective than variable valve timing methods of varying compression ratio in most applications.
A single-ended barrel engine design is also advantageous because it allows piston motion to be independently optimized for the intake, compression, combustion and exhaust cycles. This level of optimized piston motion is not possible in slider-crank engines, which are restricted to sinusoidal piston motion or in double-ended barrel engines, which cannot independently optimize piston motion for each cycle.
While single-ended barrel engines provide a simple and inexpensive means of varying compression ratio and the ability independently optimize piston motion for various engine cycles, prior art single-ended barrel engines with these abilities have yet to demonstrate a piston structure that is both structurally and kinematically feasible at normal engine speeds. Prior art single-ended barrel engines employ single-ended or double-ended, single roller piston designs that lack critical crosshead and roller support qualities needed for a feasible design.
The present invention provides improvements to barrel engines by mating the simplified variable compression ratio and optimized piston motion abilities of a single-ended barrel engine with a rigid and durable crosshead piston design. A unique double-ended, double roller piston is employed that uses one end for combustion and the other end as a crosshead guide means to reduce side loading on the piston. In some embodiments, the barrel engine includes a variable compression ratio device, while in other embodiments it includes an integral supercharger. In still other embodiments, the engine includes a non-sinusoidal cam surface, which causes the combustion ends of the pistons to move non-sinusoidally. In some embodiments, these features are used in combination with one another.
In one embodiment, the internal combustion barrel engine includes an engine housing with a first end and a second end. An elongated power shaft is longitudinally disposed in the engine housing and defines a longitudinal axis of the engine. A combustion cylinder and a guide cylinder are spaced apart and disposed on a common cylinder axis that is generally parallel to the central axis. The cylinders each have an inner end and an outer end, with the inner ends being closer to each other. The outer end of the combustion cylinder is closed. An intake system is operable to introduce a mixture of air and/or fuel into the combustion cylinder. A track is supported between the inner ends of the combustion cylinder and the guide cylinder. The track has an undulating cam surface. The track is moveable such that the portion of the cam surface most directly between the inner ends of the cylinders undulates toward and away from the inner end of the combustion cylinder. A double-ended piston includes a combustion end moveably disposed in the combustion cylinder such that a combustion chamber is defined between the combustion end of the piston and the closed end of the combustion cylinder. A guide end of the piston is moveably disposed in the guide cylinder. A midportion of the piston extends between the combustion end and the guide end. The midportion is in mechanical communication with the guide surface of the track such that as the track moves, the midportion urges the combustion end of the piston outwardly within the combustion cylinder to compress the mixture in the combustion chamber and allows the combustion end of the piston to move inwardly within the combustion chamber as the mixture within the combustion chamber expands. The guide end moves with the midportion such that as the combustion end moves outwardly, the guide end moves inwardly in the guide cylinder, and as the combustion end moves inwardly, the guide end moves outwardly. The guide end and the guide cylinder cooperate to guide the motion of the double-ended piston. A variable compression device is operable to move the track axially towards and away from the inner end of the combustion cylinder so as to adjust the compression ratio. Combustion occurs only in the combustion cylinder and does not occur in the guide cylinder.
In one alternative embodiment, the guide end of the piston is a pumping end and the guide cylinder is a pumping cylinder with a closed outer end. The pumping end and the pumping cylinder cooperate to compress a gas. The engine further includes a valve assembly for providing the gas to the pumping cylinder and venting compressed gas from the pumping cylinder. A compressed gas conduit is in fluid communication with the valve assembly and the intake system such that the compressed gas from the pumping cylinder is provided to the combustion chamber so as to supercharge the engine.
In another embodiment of the present invention, a barrel engine includes an engine housing with a first end and a second end. An elongated power shaft is longitudinally disposed in the engine housing and defines a longitudinal axis of the engine. A combustion cylinder and a guide cylinder are spaced apart and disposed on a common cylinder axis that is generally parallel to the central axis. The cylinders each have an inner end and an outer end with the inner ends being closer to each other. The outer end of the combustion cylinder is closed. An intake system is operable to introduce a mixture of air and/or fuel into the combustion cylinder. A track is supported between the inner ends of the combustion cylinder and the guide cylinder. The track has an undulating cam surface. The track is moveable such that the portion of the cam surface most directly between the inner ends of the cylinders undulates toward and away from the inner end of the combustion cylinder. The undulating cam surface defines a non-sinusoidal shape. A double-ended piston includes a combustion end moveably disposed in the combustion cylinder such that a combustion chamber is defined between the combustion end of the piston and the closed end of the combustion cylinder. A guide end of the double-ended piston is moveably disposed in the guide cylinder. A midportion extends between the combustion end and the guide end. The midportion is in mechanical communication with the cam surface of the tracks such that as the track moves, the midportion urges the combustion end of the piston outwardly within the combustion cylinder to compress the mixture in the combustion chamber and allows the combustion end of the piston to move inwardly within the combustion cylinder as the mixture within the combustion chamber expands. The motion of the piston is non-sinusoidal. The guide end moves with the midportion such that as the combustion end moves outwardly, the guide end moves inwardly in the guide cylinder and as the combustion end moves inwardly, the guide end moves outwardly. The guide end and the guide cylinder cooperate to guide the motion of the double-ended piston. Combustion occurs only in the combustion cylinder and does not occur in the guide cylinder.
In an alternative embodiment, the engine further includes a variable compression ratio device operable to move the track axially towards and away from the inner end of the combustion cylinder so as to adjust the compression ratio. In yet a further alternative embodiment, the guide end of the piston comprises a pumping end and the guide cylinder comprises a pumping end and the guide cylinder comprises a pumping cylinder with a closed outer end. The pumping end and the pumping cylinder cooperate to compress a gas. The engine further comprises a valve assembly for providing a gas to the pumping cylinder and venting compressed gas from the pumping cylinder. A compressed gas conduit is in fluid communication with the valve assembly and the intake system such that the compressed gas from the pumping cylinder is provided to the combustion chamber so as to supercharge the engine.